Although much recent attention has focused on understanding correlates to physical activity, increasing physical activity through physical education in schools, and modifying the built environment to promote more active living, there are many more questions than answers, and passive activity, overweight and obesity rates continue to grow. This grant mechanism will allow for essential program and measurement development prior to submission of a larger R01 grant. The two main purposes of this R21 are to develop (1) an innovative and collaborative approach to promote physically active leisure among middle school youth and (2) an efficient, reliable and valid measure of physical activity using cutting edge measurement and statistical techniques. Specifically we aim to: (a) Revise and further develop an existing curriculum to promote physically active leisure with an interdisciplinary team of collaborators from the university and community; (b) Develop a valid, reliable, and efficient approach to measuring physical activity in a large sample of youth; and (c) Conduct two sequential pilot studies of the intervention. The overall strategy is to take a promising, evidence based program (TimeWise: Taking Charge of Leisure Time) from an efficacy trial and work with a team of community collaborators to systematically modify and expand the program to promote physically active leisure and decrease sedentary activity in the school and community. [unreadable] [unreadable] [unreadable] [unreadable]